1. Field of the Invention
This invention is in the field of automatic calibration of magnetic compasses, such as induction and Hall effect compasses, and more particularly to the calibration of compasses mounted in a host vehicle that has permanent and induced magnetic fields.
2. Description of the Prior Art
Various sources distort the earth's magnetic field as seen by a magnetic compass mounted in a host vehicle. The purpose of calibrating a magnetic compass is to determine the amount of distortion and to provide a corresponding correction. The two basic sources of distortion are the permanent and induced magnetism of the host vehicle. In addition, the non-ideal nature of the magnetic sensor itself contributes effects which require correction. Numerous efforts have been made to provide these corrections. These include various methods of establishing or estimating a correction signal and applying a feedback signal to bucking coils coupled to the compass windings, the use of a gyrocompass in conjunction with the compass windings, and applying estimated compensation values to the signals from the compass windings. These efforts have been largely unsatisfactory since, while perhaps recognizing the complexity of the problem, they are only partial and inadequate solutions or are misdirected and no solution.